The invention relates to a method and apparatus for the destruction of weeds growing in and around crop rows without destruction of the crops growing therein. U.S. Pat. No. ',919,806 discloses a method and apparatus that is suitable for the treatment of crop rows to kill weeds growing in and around the crop rows, said U.S. Pat. No. 3,919,806 disclosure taking advantage of height discrepancy between weeds and crop plants within the crop rows themselves, and providing a plurality of individually adjustable spring members extending between the crop rows for contacting of all plants within the crop rows. While the method and structure shown in U.S. Pat. No. 3,919.806 are suitable for use with many crop plants, for some crop plants they do not achieve maximum weed destruction. In contradistinction to the method of U.S. Pat. No. 3,919,806 wherein contact of crop plants with current-carrying spring members was avoided, according to the present invention all plants -- including crop plants -- within and around the crop rows are contacted with current-carrying members, the spring members being so shaped and dimensioned according to the present invention so that the dwell time of contact between the spring members and relatively flexible weeds is greater than the dwell time of contact between the spring members and relatively stiff crop plants so that the weeds receive sufficient electrical energy to result in destruction thereof, while the crop plants do not receive sufficient electrical energy to result in destruction thereof.
According to the present invention the crop plants will generally receive significantly less electrical energy than the weeds, and when this is combined with the generally greater resistant of crop plants to destruction by electrical energy than weeds of generally the same height, the desired result of weeds destruction without crop plants destruction is achieved.
Other prior art proposals have suggested attempting to destroy only undesirable plants while leaving crop plants unharmed, as shown in U.S. Pat. No. 2,750,712, and 2,682,729. In both of these Patents the same assumption is made as according to the present invention -- that is that the crop plants that will be growing will be stronger than the undesirable plant growth so that they will have a tendency to deflect a current-carrying member while the undesirable plant growths will not. In both of these patents, however, the structure was designed so that no current-carrying portion of the machine ever touched the crop plants but rather only plants that were bent by the current-carrying portions were touched with current. In order to provide such structures fairly complicated insulator members were provided associated with the current-carrying portions, and for the destruction of undesirable plants between crop rows mechanical means were provided rather than electrical means.
According to the present invention, it is believed that as good or better weed destruction will result than according to the inventions in U.S. Pat. Nos. 2,750,712 and 2,682,729, while much simplier apparatus is provided for effecting the destruction, electrical energy being used to destroy essentially all undesirable plants in and around the crop rows. According to the present invention an electrically conductive spring member is provided disposed in a generally horizontal plane and connected up to a high voltage source of electricity, the spring member having a spring constant such that relatively stiff crop plants will deflect the spring member while relatively flexible weeds will not deflect the spring member. No insulating structures need be provided around the spring member since the spring member will be brought into contact with substantially all the plants in the crop rows and surrounding area by moving the spring member relative to the crop rows parallel to the crop rows. Destruction of the weeds results while destruction of the crop plants does not -- despite the fact that the both are touched by the current-carrying portions of the spring members -- since a larger dwell time of contact between the spring members and the relatively flexible weeds is provided than the dwell time of contact between the spring members and the relatively stiff crop plants. This difference in dwell times of contact combined with the generally greater resistance of the crop plants to electrical energy destruction than the weeds, results in the destruction of one but not the other. The decrease in dwell time of contact with the crop plants as opposed to the weeds is accomplished by providing each spring member so that it has one end connected to supporting member with a first portion adjacent the connecting end making a first angle .alpha. with a line along the direction of movement of the spring member, and a free end connected to a second portion adjacent the free end, the second portion making a second angle .beta. with a line along the direction of movement of the spring member, the second angle .beta. being substantially greater than the first angle .alpha.', and by disposing the connected end of the spring member between crop rows while the free end extends into a crop row during movement of the spring to effect contacting. The angle .alpha. preferably is about 35.degree. to 40.degree., while the angle .beta. is about 70.degree. to 80.degree..
Preferably a plurality of spring members are provided operatively associated with a vehicle, a generally horizontally extending bar generally perpendicular to the direction of travel of the vehicle and supported by the vehicle being provided with the spring members mounted to the bar by means for mounting the spring members so that they are disposed in generally horizontal planes. Each mounting means supports two members, and the mounting means are spaced from each other a distance generally equal to the spacing between adjacent crop rows so that a mounting means is generally centered in each furrow between crop rows. The length of the first portion of the spring member making the angle .alpha. is significantly greater than the length of the second portion of the spring member making the angle .beta.. Since the second portion is relatively short and since it makes a relatively great angle with respect to a line along the direction of movement of the vehicle, the crop plants will be touched only briefly before they deflect the spring member out of engagement therewith. On the other hand, the weeds between the rows will be contacted by the relatively long first portion of the spring member, and weeds both within the crop rows and around the crop rows will be deflected by the spring members so that they are bent and contact the spring members along the entire length thereof as the spring members move forwardly. Particular means are provided for adjustably mounting the spring members to the mounting means, and for adjusting the vertical position of the mounting means.
In some circumstances, where many weeds will be encountered that are significantly greater in height than the crop plants within the crop rows, it is also desirable to provide a conductive generally horizontally extending bar perpendicular to the direction of travel of the vehicle supported by the vehicle and located vertically above the spring members. The bar is operatively connected to a higher voltage source than the spring members since the plants which will be contacted thereby generally require a larger input of electrical energy to result in destruction thereof than the plants contacted by the spring members. The bar preferably is at a voltage of 15 to 30 kilovolts, while the spring members are at a approximately 1/3 the voltage of the bar, or at approximately 5 to 10 kilovolts.
It is a primary object of the present invention to provide a simplified method and apparatus for electrically destroying weeds growing in and around crop rows while not destroying the crop plants. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.